I don't know, you may notice that when you are outside, your dog may smell something in the grass, and roll his face in it, then smell it again, and roll his face in it again. I saw Scruffy do this many times, and so I went to the one spot that he was doing this, and it was bird poop!!! He has done this many times. I think, like someone else said, that they like the scent they are rolling in, and want it on themselves
